Perfluoroelastomers

ABSTRACT

Perfluoroelastomers, curable by peroxidic route, obtainable by polymerizing the following monomers:  
     a) tetrafluoroethylene (TFE);  
     b) fluorovinylethers of general formula: 
     CFX═CXOCF 2 OR  (I) 
     c) bis-olefins having general formula: 
     R I   1 R I   2 C═CR I   3 —Z—CR I   4 ═CR I   5 R I   6   (IA) 
     d) optionally, one or more fluorinated olefinic comonomers selected from C 2 -C 8  perfluoroolefins, perfluoroalkylvinylethers (PAVE) CF 2 ═CFOR 2   f , perfluoro-oxyalkylvinylethers CF 2 ═CFOX a ,  
     said perfluoroelastomers comprising iodine and/or bromine atoms in the chain and/or in end position, said halogen atoms deriving from “cure site” comonomers and/or from chain transfer agents used in polymerization.

[0001] The present invention relates to perfluoroelastomers having avery good combination of mechanical properties, compression set and atlow temperature properties and to the process for preparation thereof.

[0002] It is well known that perfluoroalkylvinylethers are generallyused as monomers for the copolymerization with tetrafluoroethylene (TFE)to obtain perfluoroelastomers which are used in the space-, oil-,petrochemical and semiconductor industry. The introduction ofperfluorovinylether high amounts in crosslinkable fluoroelastomersimplies elasticity properties at low temperature of fluorinated rubbers.

[0003] The need was felt to have available perfluoroelastomers havingimproved properties at low temperatures in combination with goodmechanical and compression set properties.

[0004] To solve said technical problem fluorovinylethers with variousstructural properties have been proposed in the prior art. However fromthe prior art the obtained perfluoroelastomers do not show thecombination of the above properties.

[0005] U.S. Pat. No. 3,132,123 describes the preparation ofperfluoroalkylvinylethers, of the respective homopolymers and copolymerswith TFE. The homopolymers are obtained under extreme experimentalconditions, by using polymerization pressures from 4,000 to 18,000 atm.The homopolymer of the perfluoromethylvinylether (MVE) is an elastomer:however its Tg is not sufficiently low. The general formula of thedescribed vinylethers is the following:

CF₂═CFOR⁰ _(F)

[0006] wherein R⁰ _(F) is a perfluoroalkyl radical preferably from 1 to5 carbon atoms.

[0007] U.S. Pat. No. 3,450,684 relates to vinylethers of formula:

CF₂═CFO(CF₂CFX⁰O)_(n′)CF₂CF₂X⁰

[0008] wherein X⁰=F, Cl, CF₃, H; n′ can range from 1 to 20.

[0009] Homopolymers obtained by UV polymerization are also described.The exemplified copolymers are not characterized with their mechanicaland elastomeric properties at low temperatures.

[0010] U.S. Pat. No. 3,817,960 relates to the preparation andpolymerization of perfluorovinylethers of formula:

CF₃O(CF₂O)_(n″)CF₂CF₂OCF═CF₂

[0011] wherein n″ can range from 1 to 5. Characterization data on theabove properties are not described.

[0012] U.S. Pat. No. 4,487,903 relates to the fluoroelastomericcopolymer preparation wherein perfluorovinylethers of formula:

CF₂═CF(OCF₂CFY⁰)_(n) ⁰OX²

[0013] are used, wherein n⁰ ranges from 1 to 4; Y⁰=F, Cl, CF₃, H; X² canbe C₁-C₃ perfluoroalkyl, C₁-C₃ ω-hydroperfluoroalkyl, C₁-C₃ω-chloroperfluoroalkyl. The polymer has a fluorovinylether unit contentranging from 15 to 50% by moles. Said vinylethers give copolymers havingat low temperatures properties superior to those of the aboveperfluorovinylethers of PVE (perfluoropropylvinylether) and MVE type.Also in this case data relating to the above properties of the curedelastomer are not indicated.

[0014] EP 130,052 describes the polymerization of theperfluorovinylpolyethers (PVPE) which leads to the obtainment ofamorphous perfluoropolymers having a T_(g) ranging from −15° to −100° C.The described polymers have T_(g) values which reach −76° C.; thefurther T_(g) decrease is obtained by using perfluoropolyethers asplasticizers. In the patent copolymers and terpolymers of TFE and MVEwith vinylethers (PVPE) of formula:

CF₂═CFO(CF₂CF(CF₃)O)_(n′″)R⁰ _(f′)

[0015] are described, wherein n′″ ranges from 3 to 30 and R⁰ _(f′) is aperfluoroalkyl. Due to purification difficulties, the used vinylethersare mixtures of vinylethers with different values of n′″. According tothis patent the most marked effect on the T_(g) decrease is shown whenn′″ is equal to or higher than 3, preferably higher than 4.

[0016] U.S. Pat. No. 4,766,190 relates to the polymerization ofperfluorovinylpolyethers (PVPE), similar to those described in U.S. Pat.No. 4,487,903, with TFE and low percentages of perfluoro propene, toincrease the mechanical properties of the obtained polymers. Noimprovement of the mechanical and elastomeric properties at lowtemperatures is described.

[0017] U.S. Pat. No. 5,268,405 discloses the preparation ofperfluorinated rubbers having a low Tg, by using perfluoropolyethershaving a high viscosity as plasticizers of perfluorinated rubbers(TFE/MVE copolymers). The obtained manufactured articles have thedrawback that during the use, exudations of the perfluoropolyethers(PFPE) take place, in particular when PFPE has low molecular weight (lowviscosity): in the patent it is therefore disclosed the use of PFPEhaving high viscosity; those having low viscosity must be previouslyremoved.

[0018] U.S. Pat. No. 5,401,818 relates to the perfluorovinyletherpreparation of formula:

R¹ _(f)(OCF₂CF₂CF₂)_(m′)—OCF═CF₂

[0019] (wherein R¹ _(f) is a C₁-C₃ perfluoroalkyl radical; m′ is aninteger raanging from 1 to 4) and of the respective copolymers havingimproved properties at low temperature. The preparation of saidperfluorovinylethers requires also a perfluorination with elementary F₂which from the industrial point of view requires supplementary processunities.

[0020] Furthermore it is well known that by increasing theperfluorooxyalkylene units which are part of the sideperfluorooxyalkylene substituent of perfluorooxyalkylvinylethers, the Tgof the obtained amporphous copolymers decreases. However it is notpossible to obtain polymers with the optimal combination of the aboveproperties.

[0021] The amorphous copolymers of TFE with perfluoromethylvinyletherhave T_(g) of about 0° C. or a little lower (Maskornik, M. et al.“ECD-006 Fluoroelastomer—A high performance engineering material”. Soc.Plast Eng. Tech. Pao. (1974), 20, 675-7). The extrapolated value of theMVE homopolymer T_(g) is of about −5° C. (J. Macromol. Sci.-Phys.,B1(4), 815-830, Dec. 19-67).

[0022] In patent application EP 1,148,072 fluorovinylethers allowing tolower the Tg of the respective copolymers are described, but themechanical and elastomeric properties of the obtained manufacturedarticles are not described.

[0023] The perfluoroelastomers described in the prior art do not showthe optimal combination of the above properties, in particular it wouldbe desirable to have available perfluoroelastomers which when cured showthe following combination of properties:

[0024] good mechanical and elastomeric properties,

[0025] high resistance to low temperatures such as for example shown byTR 10 (ASTM D 1329 method),

[0026] much lower Tg with respect to vinylethers having the same oxygennumber and carbon atoms,

[0027] maintenance of good mechanical and elastomeric properties even athigh temperatures to have a high thermal range of the perfluoroelastomeruse,

[0028] higher productivity of perfluoroelastomer in Kg ofpolymer/(hour×liter of water).

[0029] The Applicant has surprisingly and unexpectedly found that it ispossible to solve the above technical problem as described hereinafter.

[0030] An object of the present invention are perfluoroelastomers,curable by peroxidic route, obtainable by polymerizing the followingmonomers:

[0031] a) tetrafluoroethylene (TFE);

[0032] b) fluorovinylethers of general formula:

CFX═CXOCF₂OR  (I)

[0033] wherein

[0034] R has the following meanings:

[0035] C₂-C₆ linear or branched (per)fluoroalkyl,

[0036] C₅-C₆ cyclic (per)fluoroalkyl,

[0037] C₂-C₆ linear or branched (per)fluoro oxyalkyl, containing fromone to three oxygen atoms,

[0038] X=F, H;

[0039] c) bis-olefins having general formula:

R^(I) ₁R^(I) ₂C═CR^(I) ₃—Z—CR^(I) ₄═CR^(I) ₅R^(I) ₆  (IA)

[0040]  wherein

[0041] R^(I) ₁, R^(I) ₂, R^(I) ₃, R^(I) ₄, R^(I) ₅, R^(I) ₆ equal to ordifferent from each other, are H or C₁-C₅ alkyl;

[0042] Z is a C₁-C₁₈ linear or branched alkylene or C₄-C₁₈ cycloalkyleneradical, optionally containing oxygen atoms, preferably at leastpartially fluorinated, or a (per)fluoropolyoxyalkylene radical;

[0043] d) optionally, one or more fluorinated olefinic comonomersselected from the following:

[0044] C₃-C₈ perfluoroolefins, such hexafluoropropene (HFP), and/orchlorotrifluoroethylene (CTFE);

[0045] perfluoroalkylvinylethers (PAVE) CF₂═CFOR² _(f′) wherein R² _(f)is a C₁-C₆ perfluoroalkyl, for example trifluoromethyl,heptafluoropropyl;

[0046] perfluoro-oxyalkylvinylethers CF₂═CFOX^(a), wherein X^(a) is aC₁-C₁₂ alkyl, or a C₁-C₁₂ oxyalkyl, or a C₁-C₁₂ (per)fluoro-oxyalkylhaving one or more ether groups, for example perfluoro-2-propoxy-propyl;

[0047] said perfluoroelastomers comprising halogen atoms selected fromiodine and/or bromine in the chain and/or in end position, said iodineand/or bromine atoms deriving from “cure site” comonomers and/or fromchain transfer agents used in polymerization.

[0048] The preferred fluorovinylethers component b) are those of generalformula:

CFX═CXOCF₂OCF₂CF₂Y  (II)

[0049] wherein Y=F, OCF₃; X as above.

[0050] The perfluorovinylethers of formula:

CF₂═CFOCF₂OCF₂CF₃  (MOVE 1)

CF₂═CFOCF₂OCF₂CF₂OCF₃  (MOVE 2)

[0051] are the most preferred.

[0052] Preferably in the bis-olefin component c) of formula (IA) R^(I)₁, R^(I) ₂, R^(I) ₃, R^(I) ₄, R^(I) ₅, R^(I) ₆are hydrogen and Z is aC₄-C₁₂ perfluoroalkylene radical or a (per)fluoropolyoxyalkylene radicalof formula:

—(Q)_(p)—CF₂O—(CF₂CF₂O)_(ma)(CF₂O)_(na)—CF₂—(Q)_(p)—  (IIA)

[0053] wherein:

[0054] Q is a C₁-C₁₀ alkylene or oxyalkylene radical, preferablyselected from —CH₂OCH₂—; —CH₂O(CH₂CH₂O)_(s)CH₂—, s being=an integer from1 to 3;

[0055] p is an integer and is zero or 1;

[0056] ma and na are numbers such that the ma/na ratio is from 0.2 to 5,the molecular weight of the (per)fluoropolyoxyalkylene radical offormula (IIA) being from 500 to 10,000, preferably from 1,000 to 4,000.More preferably the bis-olefin has formula:

CH₂═CH—(CF₂)_(t0)—CH═CH₂

[0057] wherein t0 is an integer from 6 to 10 carbon atoms.

[0058] The iodine and/or bromine atoms in the chain and/or in endposition of the polymer can be introduced by brominated and/or iodinated“cure site” comonomers, such for example the following:

[0059] C₂-C₁₀ bromo and/or iodo olefins, containing at least one atom,preferably from one to three bromine and/or iodine atoms,

[0060] C₁-C₁₀ linear or branched (per)fluoroalkylvinylethers and/or(per)fluorooxyalkylvinylethers containing at least one iodine and/orbromine atom.

[0061] The iodine and/or bromine atom in the polymer end position can beintroduced also using iodinated and/or brominated chain transfer agents,such as for example the following:

[0062] compounds of formula R^(b) _(f)(I)_(x)(Br)_(y), wherein R^(b)_(f) is a (per)fluoroalkyl or a (per)fluorochloroalkyl having from 1 to8 carbon atoms, while x and y are integers comprised between 0 and 2,with 1≦x+y≦2;

[0063] iodides and/or bromides of alkaline or alkaline-earth metals.

[0064] Preferably the perfluoroelastomer contains iodine atoms in thechain and/or in end position.

[0065] The preferred optional component d) is perfluoromethylvinylether(MVE) having formula CF₂═CF—O—CF₃.

[0066] As said, the perfluoropolymers of the invention show thecombination of the above properties.

[0067] In particular the decrease of Tg obtained by using thevinylethers component b) is due to the presence of the (—OC—F₂O) unitdirectly linked to the unsaturation. Besides it has been found that saidunit increases the reactivity of the vinylether component b).

[0068] The advantages of the perfluoroelastomers of the invention can besummarized as follows:

[0069] improved mechanical and elastomeric properties;

[0070] very good reactivity of the fluorovinylethers component b), in Kgof polymer/(hour liter of water);

[0071] low Tg;

[0072] low TR 10.

[0073] The amount of fluorovinylethers component b) to obtain theperfluoroelastomers of the invention must be such to lead to thecrystalline site disappearance so to obtain an amorphous copolymer.

[0074] Generally the amount of units deriving from the fluorovinylethercomponent b) which allows to obtain amorphous polymers is preferablyhigher than 15% by moles, more preferably higher than 20% by moles.There are no limits to the maximum amount of b): molar amounts up to80-90% can generally be used. If in the polymer, besides units derivingfrom the fluorovinylether component b), units deriving from the optionalmonomers component d) are present, the total molar amount of b)+d) mustbe higher than 15%, preferably higher than 20% by moles. The totalamount of b)+d) can reach percentages of 80-90% by moles.

[0075] The amount of units in the chain deriving from the bis-olefincomponent c) is generally from 0.01 to 2.0% by moles, preferably from0.05 to 0.8% by moles.

[0076] The amount of units deriving from brominated and/or iodinated“cure-site” comonomers in the final compound is from 0 to 5% by moles.

[0077] The iodine and/or bromine amount from transfer agent present inthe chain end groups is from 0% to 2% by weight, preferably from 0.05%to 0.8% by weight.

[0078] The total amount of iodine and/or bromine present in theperfluorinated polymer is in the range 0.05%-4% by weight.

[0079] The perfluoroelastomers of the invention are TFE-basedcopolymers, wherein TFE is copolymerized with the fluorovinyletherscomponent b) and with the bisolefin component c); wherein also one ormore comonomers selected from component d) can optionally be present.

[0080] The preferred monomeric compositions (% by moles) are thefollowing:

[0081] TFE 40-85

[0082] component b) 1-50, pref. 5-40

[0083] component c) 0.01-2

[0084] iodine amount (in % by weight) 0.05-0.6

[0085] component d) 0-50

[0086] the sum of the molar percentages of component b)+component d)being such to give an amorphous polymer, said sum being higher than 15%,preferably higher than 20%, and the sum of the molar percentages of themonomers being equal to 100%.

[0087] The bis-olefins component c) of formula (IA) wherein Z is analkylene or cycloalkylene radical can be prepared as for exampledescribed by I. L. Knunyants et al. in Izv. Akad. Nauk. SSR, Ser. Khim.1964(2), 384-6, while the bis-olefins containing(per)fluoropolyoxyalkylene sequences are obtainable by following thereactions reported in U.S. Pat. No. 3,810,874.

[0088] The brominated and/or iodinated “cure-site” comonomers are forexample described in U.S. Pat. No. 4,035,565 and U.S. Pat. No.4,694,045, U.S. Pat. No. 4,745,165, U.S. Pat. No. 4,564,662 and EP199,138.

[0089] For the iodinated and/or brominated chain transfer agents see forexample U.S. Pat. No. 4,243,770 and U.S. Pat. No. 4,943,622.

[0090] For the chain transfer agents formed by iodides and/or bromidesof alkaline or alkaline-earth metals see U.S. Pat. No. 5,173,553.

[0091] The preparation of perfluoroelastomers of the present inventionis carried out by copolymerization of the monomers in aqueous emulsionin the presence of an emulsion, dispersion or microemulsion ofperfluoropolyoxyalkylenes, according to U.S. Pat. No. 4,789,717 and U.S.Pat. No. 4,864,006. Preferably the synthesis is carried out in thepresence of perfluoropolyoxyalkylene microemulsion.

[0092] According to well known methods of the prior art, radicalinitiators, for example, alkaline or ammonium persulphates,perphosphates, perborates or percarbonates, optionally in combinationwith ferrous, cupreous or silver salts, or of other easily oxidizablemetals, are used. In the reaction medium also surfactants of varioustype are optionally present, among which the fluorinated surfactants offormula:

R³ _(f)—X⁻M⁺

[0093] are particularly preferred, wherein R³ _(f) is a C₅-C₁₆(per)fluoroalkyl chain or a (per)fluoropolyoxyalkyl chain, X⁻ is —COO⁻or —SO₃ ⁻, M⁺ is selected from: H⁺, NH₄ ⁺, an alkaline metal ion. Amongthe most commonly used we remember: ammonium perfluorooctanoate,(per)fluoropolyoxyalkylenes ended with one or more carboxyl groups, etc.See U.S. Pat. No. 4,990,283 and U.S. Pat. No. 4,864,006.

[0094] The polymerization reaction is generally carried out attemperatures in the range 25° C.-150° C., at a pressure comprisedbetween the atmospheric one up to 10 MPa.

[0095] Alternatively or in combination with the chain transfer agentscontaining iodine and/or bromine, other chain transfer agents known inthe prior art, as ethyl acetate, diethylmalonate, etc., can be used.

[0096] When the polymerization is over, the perfluoroelastomer isisolated from the emulsion by conventional methods, as the coagulationby addition of electrolytes or by cooling.

[0097] The perfluoroelastomers object of the present invention are curedby peroxidic route, according to known techniques, by addition of asuitable peroxide capable to generate radicals by heating.

[0098] Among the most commonly used peroxides the following arementioned: dialkylperoxides, such for example, di-terbutyl-peroxide and2,5-dimethyl-2,5-di(terbutylperoxy)hexane; di-cumyl peroxide, dibenzoylperoxide; diterbutyl perbenzoate;di-[1,3-dimethyl-3-(terbutylperoxy)butyl]carbonate. Other peroxidicsystems are described for example in European patent applications EP136,596 and EP 410,351.

[0099] To the curing blend other compounds are then added, such as:

[0100] (A) curing coagents, in an amount generally in the range 0.5-10,preferably 1-7%, by weight with respect to the polymer; among them thosecommonly used are: bis-olefins of formula (IA); triallyl-cyanurate,triallyl-isocyanurate (TAIC), tris (diallylamine)-s-triazine;triallylphosphite; N,N-diallyl-acrylamide;N,N,N′,N′-tetraallyl-malonamide; tri-vinyl-isocyanurate; and4,6-tri-vinyl-methyltrisiloxane, etc.: TAIC and the bis-olefin offormula:

CH₂═CH—(CF₂)₆—CH═CH₂

[0101]  are particularly preferred;

[0102] (B) optionally a metal compound, in an amount in the range 0-15%,preferably 2-10%, by weight with respect to the polymer, selected fromoxides and hydroxides of divalent metals, such for example Mg, Zn, Ca orPb, optionally combined with a weak acid salt, such for examplestearates, benzoates, carbonates, oxalates or phosphites of Ba, Na, K,Pb, Ca;

[0103] (C) optionally acid acceptors, in an amount from 0 to 10% byweight with respect to the polymer, of the non metal oxide type, such1,8 bis dimethyl amino naphthalene, octadecylamine etc. as described inEP 708,797;

[0104] (D) optionally conventional additives, such thickeners, pigments,antioxidants, stabilizers and the like, the amount of each of saidadditives being between 0 and 10% by weight with respect to the polymer;

[0105] (E) optionally fillers in amounts from 0 to 80% by weight withrespect to the polymer, preferably from 15 to 50% by weight, such forexample carbon black, silica, barium sulphate, titanium dioxide, etc.Fillers of semicrystalline fluoropolymers, such PTFE, MFA and PFA, canalso be present.

[0106] The copolymers of the invention when cured by peroxidic routeshow a very good combination of properties, in particular they satisfythe following test: a copolymer having the following composition in percent by moles:

[0107] tetrafluoroethylene (TFE) 69.9%

[0108] fluorovinylethers component b) MOVE 1 30%

[0109] bis-olefin component c) of formula CH₂═CH—(CF₂)₆—CH═CH₂ 0.1%

[0110] having as attack site for the peroxidic crosslinking an iodineamount, in per cent by weight, equal to 0.24%, the iodine being presenton the chain end groups through the iodinated transfer agent1,4-diiodoperfluorobutane (C₄F₈I₂), in a compound containing for 100 phrof perfluoroelastomer:

[0111] Luperco® 101 XL* 1.5

[0112] DRIMIX® TAIC** 2

[0113] ZnO 5

[0114] Black MT®N990 20

[0115] containing 45% by weight of2,5-dimethyl-2,5-di(ter-butylperoxy)hexane

[0116] containing 75% by weight of TAIC

[0117] cured in press for 10 minutes at 160° C., subjected to post-curein an air forced circulation stove at 230° C. for 4 hours, after awarming step from room temperature to 230° C. lasting one hour, showsthe following combination of properties: stress at break (ASTM D412-83) >13 MPa elongation at break (ASTM D 412-83) >130% hardness(shore A) >65 compression set (ASTM D 395) on O-ring <40% at 200° C. for70 h TR 10 (ASTM D 1329) <−20° C.

[0118] The synthesis process of the (per)fluorovinylethers component b)comprises the following steps:

[0119] a′) initial reaction of the hypofluorite with a fluorinatedolefin of formula R₁R₂C═CR₃R₄ to give the hypofluorite

CF₂(OF)₂+R₁R₂C═CR₃R₄→F—CR₁R₂—CR₃R₄—OCF₂OF  (VI)

[0120] b′) reaction of the hypofluorite with a second fluorinated olefinof formula R₅R₆C═CR₇R₈ to give the intermediate

F—CR₁R₂—CR₃R₄—OCF₂O—CR₅R₆—CR₇R₈—F,

F—CR₁R₂—CR₃R₄—OCF₂OF+R₅R₆C²=C¹R₇R₈----->F—CR₁R₂—CR₃R₄—OCF₂O—C²R₅R₆—C¹R₇R₈—F  (VII)

[0121] c′) dehalogenation or dehydrohalogenation and obtainment of theperfluorovinylethers.

[0122] In said synthesis scheme:

[0123] with reference to the formula of compound (VII):

[0124] R₁, R₄, equal or different, are H, F; R₂, R₃, equal or differentare H, Cl at the following conditions: (1) when the final reaction is adehalogenation R₂, R₃=Cl, (2) when the final reaction is adehydrohalogenation one of the two substituents R₂, R₃ is H and theother is Cl;

[0125] R₅, R₆, R₇, R₈ are:

[0126] F, or one of them is a C₁-C₄ linear or branched perfluoroalkylgroup, or a C₁-C₄ linear or branched perfluorooxyalkyl group containingfrom one to three oxygen atoms, or R₅ and R₇, or R₆ and R₈, are linkedeach other to form with C² and C¹ a C₅-C₆ perfluoroalkyl cycle;

[0127] when one of the radicals R₅ to R₈ is a C₂-C₄linear or branchedfluoroalkyl, or a C₂-C₄ linear or branched fluorooxyalkyl containingfrom one to three oxygen atoms, one or two of the other R₅ to R₈ are Fand one or two of the remainders, equal to or different from each other,are selected from H, Cl; when the substituents selected from H and Clare two, they are both linked to the same carbon atom; when R₅ and R₇,or R₆ and R₈, are linked each other to form with C² and C¹ a C₅-C₆fluoroalkyl cycle, one of the two free substituents R₆, R₈ or R₅, R₇ isF and the other is selected from H, Cl.

[0128] the fluoroalkene used in the reaction a′) is replaceable withthat of the subsequent reaction b′); in this case the meanings definedfor the substituents of the R₁-R₄ group, and respectively of the R₅-R₈group, are interchangeable each other, with the proviso that theposition of each radical of each of the two groups R₁-R₄ and R₅-R₈ withrespect to —OCF₂O— on the chain of the intermediate compound (VII), isthe same which is occupied when the synthesis takes place according tothe above scheme, and the two olefins react each in the planned steps.

[0129] In the first reaction a′) of the above scheme a hypofluorite gasflow CF₂(OF)₂, suitably diluted with an inert fluid, comes into contact,in a suitable reactor equipped with outlet, on the bottom of the same(first reactor), with a flow formed by the olefin R₁R₂C═CR₃R₄,optionally diluted in an inert fluid, to allow the chemical reaction a′)with formation of the intermediate hypofluorite (VI). To favour thereaction stoichiometry the reactants must be introduced into the reactorin an about unitary molar ratio, or with an excess of CF₂(OF)₂. Theresidence time of the mixture in the reactor can range from fewhundredths of second up to about 120 seconds in in function of theolefin reactivity, the reaction temperature and the presence of optionalreaction solvents.

[0130] The reaction temperature can range from −40° to −150° C.,preferably from −80° to −130° C.

[0131] Compound (VI) is usually not separated from the reaction crudecompound and is continuously transferred in the subsequent reactiondescribed in step b′).

[0132] The compound mixture coming out from the first reactor can beheated to room temperature before being fed to the second reactor.

[0133] In the second reaction b′) the second olefin R₅R₆C═CR₇R₈ at thepure state or in solution, reacts with the compound obtained in thefirst reaction with formation of compound (VII).

[0134] The olefin can be continuously fed so as to maintain constant itsconcentration in the reactor. The temperature of the reaction b′) canrange from −20° to −130° C., preferably from −50° to −100° C. The olefinconcentration is higher than or equal to 0.01M, preferably theconcentration is higher than 3M, more preferably also the pure compoundcan be used.

[0135] The solvents used in steps a′) and b′) are perfluorinated orchlorohydrofluorinated solvents or hydrofluorocarbons. Examples of saidsolvents are: CF₂Cl₂, CFCl₃, CF₃CF₂H, CF₃CFH₂, CF₃CF₂CF₃, CF₃CCl₂H,CF₃CF₂Cl.

[0136] In the reaction c′) compound (VII), depending on the olefins usedin steps a′) and b′), upon distillation from the reaction crudecompound, is subjected to dechlorination or to dehydrochlorination toobtain the vinylethers of formula (I).

[0137] This last step can be carried out by using reactions widelydescribed in the prior art. The suitable selection of the substituentsfrom R₁ to R₈ in the two olefins used in the synthesis allows to obtainthe vinylethers of the present invention.

[0138] The following Examples are reported with the purpose toillustrate the invention and they do not limit the scope thereof.

EXAMPLE 1 Copolymer TFE/MOVE 1 (CF₂═CF—O—CF₂—O—CF₂CF₃) 70/30% by Moles

[0139] In a 5 liter autoclave, equipped with stirrer working at 630 rpm,were introduced, after air evacuation, 3.5 liters of demineralized waterand 34.5 ml of a microemulsion obtained by mixing:

[0140] 7.5 ml of a perfluoropolyoxyalkylene having acid end group offormula:

CF₂ClO(CF₂—CF(CF₃)O)_(n)(CF₂O)_(m)CF₂COOH

[0141]  wherein n/m=10, having average molecular weight of 600;

[0142] 7.5 ml of an aqueous solution of NH₃ at 30% by volume;

[0143] 15 ml of demineralized water;

[0144] 4.5 ml of Galden® D02 of formula:

CF₃O(CF₂—CF(CF₃)O)_(n)(CF₂O)_(m)CF₃

[0145]  wherein n/m=20, having average molecular weight of 450.

[0146] The autoclave was then heated to the temperature of 80° C. andmaintained at said temperature for the whole reaction. Then 146 g ofCF₂═CF—O—CF₂—O—CF₂CF₃ (MOVE 1), 6.2 g of 1,4-diiodoperfluorobutane(C₄F₈I₂) were added. The autoclave inside is then pressurized at 5 bar(0.5 MPa) with tetrafluoroethylene (TFE). When said internal pressurevalue is reached, are introduced:

[0147] 0.35 g of ammoniumpersulphate (APS) as initiator;

[0148] 2.2 g (6.2 mmoles) of bis-olefin having formula

CH₂═CH—(CF₂)₆—CH═CH₂;

[0149]  the bis-olefin addition is carried out for a total of 20portions, each of 0.11 g, starting from the beginning of thepolymerization and for every 5% increase in the monomer conversion;

[0150] 462 g of CF₂═CF—O—CF₂—O—CF₂CF₃ (MOVE 1); the compound addition iscarried out for a total of 19 portions, each of 24.3 g, starting whenthe monomer conversion equal to 5% takes place and continuing at every5% increase in the monomer conversion.

[0151] The pressure is maintained constant for the whole polymerizationby feeding pure TFE.

[0152] After 220 minutes of reaction, corresponding to 100% of themonomer conversion, the autoclave is cooled and the latex discharged.

[0153] The so obtained latex is coagulated with an aluminum sulphatesolution (6 g of Al₂(SO₄)₃ for each liter of latex) and dried at 90° C.in an air circulating oven for 16 hours. 910 g of polymer are obtained.

[0154] By ¹⁹F-NMR analysis of the polymer hot dissolved in C₆F₆, themolar percentage of MOVE 1 in the polymer, equal to 30%, is determined.

[0155] The T_(g) determined by DSC is −25° C.

[0156] The intrinsic viscosity of the polymer in Galden® D80 is 36.7ml/g. The percentage by weight of iodine in the polymer, measured byXRF, is 0.24% by weight. The Mooney viscosity (ML(1+10′@121° C.))determined according to the ATSM D 1646 method is 27 MU.

[0157] The obtained polymer is mixed in an open roll mixer with thecrosslinking additives in phr ratios as shown in Table 1. Thecrosslinking curve, the mechanical properties, the compression set andTR 10 are reported in Table 1.

EXAMPLE 2 Copolymer TFE/MOVE 1 59/41% by Moles

[0158] In a 5 liter autoclave, equipped with stirrer working at 630 rpm,3.5 liters of demineralized water and 35 ml of the microemulsion ofExample 1, were introduced after evacuation.

[0159] The reaction mixture was heated to the temperature of 80° C.,which was maintained for the whole reaction. Then 222 g ofCF₂═CF—O—CF₂—O—CF₂CF₃ (MOVE 1), 5.5 g of 1,4-diiodoperfluorobutane(C₄F₈I₂) were added.

[0160] The autoclave inside is then pressurized at 4 bar (0.4 MPa) withtetrafluoroethylene (TFE).

[0161] It is then introduced in the autoclave:

[0162] 0.53 g of ammoniumpersulphate (APS) as initiator;

[0163] 2.6 g (7.3 mmoles) of bis-olefin having formula

CH₂═CH—(CF₂)₆—CH═CH₂;

[0164]  the bis-olefin addition is carried out for a total of 20portions, each of 0.13 g, starting from the beginning of thepolymerization and for every 5% increase in the monomer conversion;

[0165] 703 g of CF₂═CF—O—CF₂—O—CF₂CF₃ (MOVE 1); the compound addition iscarried out for a total of 19 portions each of 24.3 g, starting when themonomer conversion equal to 5% takes place and continuing at every 5%increase in the monomer conversion.

[0166] The pressure is maintained constant for the whole polymerizationby feeding pure TFE.

[0167] After 500 minutes of reaction, corresponding to 100% of themonomer conversion, the autoclave is cooled and the latex discharged.

[0168] The latex is coagulated and treated as described in Example 1obtaining 1,200 g of polymer.

[0169] By ¹⁹F-NMR analysis of the polymer hot dissolved in C₆F₆, themolar percentage of MOVE 1 in the polymer, equal to 41%, is determined.

[0170] The T_(g) determined by DSC is −31° C.

[0171] The intrinsic viscosity of the polymer in Galden® D80 is 35.8ml/g. The percentage by weight of iodine in the polymer, measured byXRF, is 0.16% by weight.

[0172] The obtained polymer is mixed in an open roll mixer with thecrosslinking additives in phr ratios as shown in Table 1. Thecrosslinking curve, the mechanical properties, compression set and TR 10are reported in Table 1.

EXAMPLE 3 Terpolymer TFE/MOVE 1 78/22% by Moles

[0173] In a 2 liter autoclave, equipped with stirrer working at 800 rpm,were introduced after air evacuation, 1.3 1 of demineral-ized water and20 ml of a microemulsion obtained by mixing:

[0174] 4.3 ml of a perfluoropolyoxyalkylene having acid end group havingthe same formula and the same molecular weight as that used in themicroemulsion of Example 1;

[0175] 4.3 ml of an aqueous solution of NH₃ at 30% by volume;

[0176] 8.8 ml of demineralized water;

[0177] 2.6 ml of Galden® D02 (formula and molecular weight in Example1).

[0178] The autoclave inside was heated to the temperature of 80° C. andmaintained at said temperature for the whole reaction. Then 33 g ofCF₂═CF—O—CF₂—O—CF₂CF₃ (MOVE 1) and 1.1 g of 1,4-diiodoperfluorobutane(C₄F₈I₂) were added in the autoclave.

[0179] The autoclave inside is then pressurized at 6 bar (0.6 MPa) withtetrafluoroethylene (TFE).

[0180] It is then introduced in the autoclave:

[0181] 0.065 g of ammoniumpersulphate (APS) as initiator;

[0182] 0.4 g (1.1 mmoles) of bis-olefin having formula

CH₂═CH—(CF₂)₆—CH═CH₂;

[0183]  the compound addition was carried out for a total of 20portions, each of 0.02 g, starting from the beginning of thepolymerization and for every 5% increase in the monomer conversion;

[0184] 5.8 g of 4-bromo-heptafluoroethylvinylether CF₂═CF—O—CF₂CF₂Br;the compound addition was carried out for a total of 20 portions, eachof 0.29 g, starting from the beginning of the polymerization and forevery 5% increase in the monomer conversion;

[0185] 104.5 g of CF₂═CF—O—CF₂—O—CF₂CF₃ (MOVE 1);

[0186]  the compound addition is carried out for a total of 19 portions,each of 5.5 g, starting when the monomer conversion equal to 5% takesplace and continuing at every 5% increase in the monomer conversion.

[0187] The pressure of 6 bar (0.6 MPa) is maintained constant for thewhole polymerization by feeding pure tetrafluoroethylene (TFE).

[0188] After 240 minutes of reaction, corresponding to 100% of themonomer conversion, the autoclave is cooled and the latex discharged.

[0189] The latex is coagulated and treated as described in Example 1obtaining 200 g of polymer.

[0190] By ¹⁹F-NMR analysis of the polymer hot dissolved in C₆F₆, themolar percentage of MOVE 1 in the polymer, equal to 22%, is determined.

[0191] The T_(g) determined by DSC is −23° C.

[0192] The intrinsic viscosity of the polymer in Fluorinert® FC-75 is28.4 ml/g. The percentage by weight of iodine and bromine in thepolymer, measured by XRF, are respectively 0.16% and 0.47% by weight.The Mooney viscosity (ML(1+10′@121° C.)) determined according to theATSM D 1646 method is 48 MU.

[0193] The obtained polymer is mixed in a roll open mixer with thecrosslinking additives in phr ratios as shown in Table 1. Thecrosslinking curve, the mechanical properties, the compression set andTR 10 are reported in Table 1.

EXAMPLE 4 (COMPARATIVE) Copolymer TFE/MOVE 1 76/24

[0194] In a 40 ml AISI-316 reactor for polymerization, equipped withmagnetic stirring, pressure transducer and inlet for the feeding anddischarge of the reactants, 250 μl of perfluoropropionylperoxide at 3%by weight of CFCl₂CF₂Cl, 9.8 mmoles of MOVE 1 and 18 mmoles oftetrafluoroethylene are introduced.

[0195] The reactor is cooled to the temperature of −196° C., evacuated,then brought again to room temperature and cooled again, the wholetwice.

[0196] At the end of the degassing operations, the reactor isthermostated at the temperature of 30° C. and the reaction mixturemaintained under magnetic stirring. The internal pressure decreases from6.4 atm to 4.7 atm in about 8 hours (reaction time).

[0197] After distillation of the unreacted monomers and polymerstripping under vacuum for 3 hours at 150° C., 1,100 mg of polymer arerecovered, which appears as a transparent and colourless rubber.

[0198] By ¹⁹F-NMR analysis of the polymer hot dissolved in C₆F₆ it isdetermined that the molar percentage of MOVE 1 in the polymer is 24%.

[0199] The T_(g), determined by DSC, is −21° C. The intrinsic viscosityof the polymer measured at 30° C. in Fluorinert® FC-75, is of 35.5 ml/g.

EXAMPLE 5 (COMPARATIVE) Copolymer TFE/β-PDE (CF₃OCF₂CF₂OCF═CF₂) 77/23

[0200] In a reactor for polymerizations equal to that described inExample 4, 250 μl of perfluoropropionylperoxide at 3% by weight inCFCl₂—CF₂Cl, 10 mmoles of β-PDE and 18 mmoles of tetrafluoroethylene arein sequence introduced.

[0201] The procedure described in the previous Example 4 is followedtill the thermostating step at the temperature of 30° C. under magneticstirring.

[0202] By ¹⁹F-NMR analysis carried out on the polymer, it is determinedthat the molar percentage of β-PDE in the polymer is 23%. The T_(g)determined by DSC is −5° C.

[0203] Said Tg value is evidently higher than that obtained in theTFE/MOVE 1 copolymer of Example 4 which contains a substantiallyidentical molar percentage of vinylether. TABLE 1 EXAMPLES 1 2 3Formulation: Luperco 101 XL phr 1.5 2 2 Drimix TAIC ″ 2 4 3 ZnO ″ 5 5 5Black MT N990 20 30 20 Iodine % by weight 0.24 0.16 0.16 Bromine % byweight 0 0 0.47 Mooney polymer ML_(121° (1+10)) 27 — 48 Mooney blendML_(121° (1+10)) 24 59 22 MDR arc 0.5°, 160° C., 12′ (ASTM D 6204-97) MLLbf.in. 0.22 0.45 0.15 MH ″ 12.4 10.3 14.2 t′2 min 0.50 0.45 0.49 ts2 ″0.63 0.64 0.64 t′50 ″ 0.86 0.97 1.60 t′90 ″ 1.81 2.35 11.4 VmaxLbf.in./min 20.0 11.8 12.2 Mechanical properties after post-cure at 230°C. for 1 + 4 h (ASTM D 412-83) M100 Mpa 5.3 5.2 8.9 Stress at break ″13.5 8.0 13.4 Elong. at break % 181 173 144 Hardness Shore A 69 72 73Compression set 200° C. for 70 h O-ring (ASTM D 395) % 32 48 50 TR 10(ASTM D 1329) ° C. −21 −26 −17

1. Perfluoroelastomers, curable by peroxidic route, obtainable bypolymerizing the following monomers: a) tetrafluoroethylene (TFE); b)fluorovinylethers of general formula: CFX═CXOCF₂OR  (I)  wherein R hasthe following meanings: C₂-C₆ linear or branched (per)fluoroalkyl, C₅-C₆cyclic (per)fluoroalkyl, C₂-C₆ linear or branched (per)fluoro oxyalkyl,containing from one to three oxygen atoms, X=F, H; c) bis-olefins havinggeneral formula: R^(I) ₁R^(I) ₂C═CR^(I) ₃—Z—CR^(I) ₄═CR^(I) ₅R^(I)₆  (IA)  wherein R^(I) ₁, R^(I) ₂, R^(I) ₃, R^(I) ₄, R^(I) ₅, R^(I) ₆equal to or different from each other, are H or C₁-C₅ alkyl; Z is aC₁-C₁₈ linear or branched alkylene or C₄-C₁₈ cycloalkylene radical,optionally containing oxygen atoms, preferably at least partiallyfluorinated, or a (per)fluoropolyoxyalkylene radical; d) optionally, oneor more fluorinated olefinic comonomers selected from the following:C₃-C₈ perfluoroolefins, such hexafluoropropene (HFP), and/orchlorotrifluoroethylene (CTFE); perfluoroalkylvinylethers (PAVE)CF₂═CFOR² _(f), wherein R² _(f) is a C₁-C₆ perfluoroalkyl, for exampletrifluoromethyl, heptafluoropropyl; perfluoro-oxyalkylvinylethersCF₂═CFOX^(a), wherein X^(a) is a C₁-C₁₂ alkyl, or a C₁-C₁₂ oxyalkyl, ora C₁-C₁₂ (per)fluoro-oxyalkyl having one or more ether groups, forexample perfluoro-2-propoxy-propyl; said perfluoroelastomers comprisingiodine and/or bromine atoms in the chain and/or in end position, saidiodine and/or bromine atoms deriving from “cure site” comonomers and/orfrom chain transfer agents used in polymerization. 2.Perfluoroelastomers according to claim 1, wherein the fluorovinyletherscomponent b) have general formula: CFX═CXOCF₂OCF₂CF₂Y  (II) wherein Y=F,OCF₃; X as above.
 3. Perfluoroelastomers according to claim 2, whereinthe perfluorovinylethers have the following formulas:CF₂═CFOCF₂OCF₂CF₃  (MOVE 1)CF₂═CFOCF₂OCF₂CF₂OCF₃  (MOVE 2) 4.Perfluoroelastomers according to claims 1-3, wherein in formula (IA) ofthe bis-olefin component c) R^(I) ₁, R^(I) ₂, R^(I) ₃, R^(I) ₄, R^(I) ₅,R^(I) ₆ are hydrogen and Z is a C₄-C₁₂ perfluoroalkylene radical or a(per)fluoropolyoxyalkylene radical of formula:—(Q)_(p)—CF₂O—(CF₂CF₂O)_(ma)(CF₂O)_(na)—CF₂—(Q)_(p)—  (IIA) wherein: Qis a C₁-C₁₀ alkylene or oxyalkylene radical, preferably selected from—CH₂OCH₂—; —CH₂O(CH₂CH₂O)_(s)CH₂—, s being=an integer from 1 to 3; p isan integer and is zero or 1; ma and na are numbers such that the ma/naratio is from 0.2 to 5, the molecular weight of the(per)fluoropolyoxyalkylene radical of formula (IIA) being from 500 to10,000, preferably from 1,000 to 4,000.
 5. Perfluoroelastomers accordingto claim 4, wherein the bis-olefin has formula: CH₂═CH—(CF₂)_(t0)—CH═CH₂wherein t0 is an integer from 6 to
 10. 6. Perfluoroelastomers accordingto claims 1-5, wherein the brominated and/or iodinated “cure site”comonomers are selected from the following: C₂-C₁₀ bromo and/or iodoolefins, containing at least one atom, preferably from one to threebromine and/or iodine atoms, C₁-C₁₀ linear or branched(per)fluoroalkylvinylethers and/or (per)fluorooxyalkylvinyletherscontaining at least one iodine and/or bromine atom. 7.Perfluoroelastomers according to claims 1-5, wherein iodine and/orbrominated chain transfer agents are selected from the following:compounds of formula R^(b) _(f)(I)_(x)(Br)_(y), wherein R^(b) _(f) is a(per)fluoroalkyl or a (per)fluorochloroalkyl having from 1 to 8 carbonatoms, while x and y are integers comprised between 0 and 2, with1≦x+y≦2; iodides and/or bromides of alkaline or alkaline-earth metals.8. Perfluoroelastomers according to claims 6-7, containing iodine atomsin the chain and/or in end position.
 9. Perfluoroelastomers according toclaims 1-8, wherein the optional component d) isperfluoromethylvinylether (MVE) CF₂═CF—O—CF₃.
 10. Perfluoroelastomersaccording to claims 1-9, wherein the amount of units deriving from thefluorovinylether component b) is higher than 15% by moles, preferablyhigher than 20% by moles.
 11. Perfluoroelastomers according to claims1-10, wherein the total amount of units deriving from thefluorovinylether component b) and from the optional monomers componentd) is higher than 15%, preferably higher than 20% by moles. 12.Perfluoroelastomers according to claims 1-11, wherein the amount ofunits in the chain deriving from the bis-olefin component c) is from0.01 to 2.0% by moles, preferably from 0.05 to 0.8% by moles. 13.Perfluoroelastomers according to claims 1-12, wherein the amount ofunits deriving from brominated and/or iodinated “cure-site” comonomersis from 0 to 5% by moles, the iodine and/or bromine amount from transferagent present in the chain end groups is from 0% to 2% by weight,preferably from 0.05% to 0.8% by weight.
 14. Perfluoroelastomersaccording to claim 13, wherein the total amount of iodine and/or brominepresent in the polymer is in the range 0.05%-4% by weight. 15.Perfluoroelastomers according to claims 1-14, having the followingmonomeric composition, in % by moles: TFE 40-85 component b) 1-50, pref.5-40 component c) 0.01-2 iodine amount (in % by weight) 0.05-0.6component d) 0-50 the sum of the molar percentages of componentb)+component d) being higher than 15%, preferably higher than 20%, andthe sum of the molar percentages of the monomers being equal to 100%.16. Blends curable by peroxidic route containing the perfluoroelastomersaccording to claims 1-15, and (A) curing coagents, in an amountgenerally in the range 0.5-10% by weight with respect to the polymer;(B) optionally a metal compound, in an amount in the range 0-15%,selected from oxides and hydroxides of divalent metals, such for exampleMg, Zn, Ca or Pb, optionally combined with a weak acid salt, such forexample stearates, benzoates, carbonates, oxalates or phosphites of Ba,Na, K, Pb, Ca; (C) optionally acid acceptors, in an amount from 0 to 10%by weight with respect to the polymer, of the non metal oxide type, such1,8 bis dimethyl amino naphthalene, octadecylamine; (D) optionallyadditives, such thickeners, pigments, antioxidants, stabilizers and thelike, the amount of each of said additives being between 0 and 10% byweight with respect to the polymer; (E) optionally fillers in amountsfrom 0 to 80% by weight with respect to the polymer, preferably from 15to 50% by weight, such for example carbon black, silica, bariumsulphate, titanium dioxide, semicrystalline fluoropolymers. 17.Perfluoroelastomers according to claims 1-16, cured by peroxidic route.18. Manufactured articles obtainable from the perfluoroelastomers ofclaim 17.